Cree XLamp XP-E MR16 Reference Design

Transcription

1 Cree XLamp XP-E MR16 Reference Design CLD-AP-76 REV 0 INTRODUCTION It is a challenge to design an efficient, high lumen, small form factor, solid-state luminaire at a reasonable cost. The limited space of an MR16 lamp means that designing the optical, thermal, and electrical components to achieve the desired requirements is not easy. This application note details the design of an MR16 lamp using Cree s XLamp XP-E LED. The goal of this design is to develop a replacement 20 W MR16 lamp meeting the ENERGY STAR requirements. In this reference design we used simulation and prototype creation to build a replacement for the traditional 20 W MR16 halogen bulb. Building on Cree s reference designs of prototype MR16 replacement lamps using XLamp MT-G and XM-L EZW LEDs 1, this design provides another possibility to create an LED-based MR16 lamp that exceeds the performance of existing halogen MR16 bulbs. TABLE OF CONTENTS Design approach/objectives... 2 The 6-step methodology Define lighting requirements Define design goals Estimate efficiencies of the optical, thermal & electrical systems Calculate the numbder of LEDs Consider all design possibilities Complete the final steps: implementation and analysis Conclusions Cree XLamp MT-G MR16 Reference Design, Application Note AP62 Cree XLamp XM-L EZW MR16 Reference Design, Application Note AP71 Copyright 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarks and EasyWhite is a trademark of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available at com. For warranty information, please contact Cree Sales at Other trademarks, product and company names are the property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. Cree, Inc Silicon Drive Durham, NC USA Tel:

2 DESIGN APPROACH/OBJECTIVES In the LED Luminaire Design Guide, 2 Cree advocates a 6-step framework for creating LED luminaires. All Cree reference designs use this framework, and the design guide s summary table is reproduced below. Step Explanation 1. Define lighting requirements The design goals can be based either on an existing fixture or on the application s lighting requirements. 2. Define design goals Specify design goals, which will be based on the application s lighting requirements. Specify any other goals that will influence the design, such as special optical or environmental requirements. 3. Estimate efficiencies of the optical, thermal & electrical systems 4. Calculate the number of LEDs needed 5. Consider all design possibilities and choose the best Design goals will place constraints on the optical, thermal and electrical systems. Good estimations of efficiencies of each system can be made based on these constraints. The combination of lighting goals and system efficiencies will drive the number of LEDs needed in the luminaire. Based on the design goals and estimated losses, the designer can calculate the number of LEDs to meet the design goals. With any design, there are many ways to achieve the goals. LED lighting is a new field; assumptions that work for conventional lighting sources may not apply. 6. Complete final steps Complete circuit board layout. Test design choices by building a prototype luminaire. Make sure the design achieves all the design goals. Use the prototype to further refine the luminaire design. Record observations and ideas for improvement. Table 1: Cree 6-step framework THE 6-STEP METHODOLOGY The major goal for this project was to create a 20 W equivalent XLamp XP-E LED-based MR16 lamp. It is meant to be a plug-in replacement for any MR16 fixture and operate with the existing low voltage power supply. 1. DEFINE LIGHTING REQUIREMENTS Table 2 shows a ranked list of desirable characteristics to address in an MR16 reference design. Importance Characteristic Units Critical Light intensity Center Beam Candle Power (CBCP) candelas (cd) Nominal beam angle Angle (deg) Electrical power Watts (W) Luminous flux Lumens (lm) Form factor Important Price $ Lifetime Hours Operating temperatures C Operating humidity % RH Correlated Color Temperature (CCT) K Color Rendering Index (CRI) 100 point scale Manufacturability Ease of installation Table 2: Ranked design criteria for MR16 replacement lamp 2 LED Luminaire Design Guide, Application Note AP15, property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 2

5 Figure 2: Binning comparison(left: XP-E, right: XP-G) Cree chose to work with the XPEWHT-H AE7, highlighted in yellow in Figure 3, in this reference design. Figure 3: XP-E color, bin and order code The XLamp XP-E LED has completed LM-80 testing, fulfilling ENERGY STAR s requirement. The XP-E has been in volume production for over two years and has become the workhorse of many LED luminaires. It is a reliable choice for an MR16 retrofit lamp. property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 5

6 Thermal Requirements Despite the XLamp XP-E LED s efficacy advantage over conventional incandescent and fluorescent lighting, as much as 80% of the input power is converted to heat. This heat needs to be dissipated efficiently to ensure LED and luminaire lumen maintenance and reliability. For a 4 W MR16 luminaire, there are many existing market thermal solutions from which to choose. For this reference design, Cree selected an existing well-designed machined aluminum heat sink with good workmanship. Our simulations and actual test results confirmed this as a good choice for this project. Figure 4: Machined aluminum heat sink Cree performed thermal simulation 6 on the design with 3 XP-E LEDs running at both 350 ma and 700 ma and found the estimated solder point temperature to be 53 C. Figure 5 shows the thermal simulation of the solder point temperature. Figure 6 shows the thermal simulation of the airflow, in the form of convection currents, around the XP-E MR16 lamp. Figure 5: Thermal simulation of temperature of XP-E MR16 Figure 6: Thermal simulation of airflow around XP-E MR16 6 Cree used NIKA EFD Pro V8.2 with Pro E Wildfire property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 6

7 Figure 7 shows the thermocouple attached to the XP-E MR16 lamp to record the solder point temperature. Figure 8 shows the measurement in progress and the temperature reading. The steady-state measurement of 60 C is a reasonable match to the thermal simulation. Figure 7: Thermocouple attached to XP-E LED Figure 8:XP-E MR16 solder point temperature measurement Based on Cree s experience with the XLamp XP-E LED and the L70 lifetime projection shown in Figure 9, we expect this design to attain both an ENERGY STAR compliant L70 rating of 25,000 hours and meet the target design goal of an L70 rating of 50,000 hours. Current Ta/Tsp (ºC) L70 (hours) 350 ma 85 96, ma* 85 90,234* 500 ma* 85 79,234* 600 ma* 85 69,575* 700 ma 85 61,094 * Interpolated values Figure 9: XP-E L70 lifetime estimate Driver Electronics Considering the traditional MR16 power requirement and for ease of retrofit, we chose to use a GU5.3 bi-pin connector with 12 VDC and 12 VAC power input. The LEDs were connected in series to achieve a higher overall Vf for better driver efficiency and to provide the constant drive current required by the LEDs to achieve consistent light output. To meet the challenge of fitting a high-efficiency driver into the compact space of an MR16 lamp base, a non-dimmable driver with simple circuit design 7 was used, shown in Figure Driver from Shen Zhen IPOWER Electronic Technology Co., Ltd. property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 7

9 A well-designed TIR optic provides high optical efficiency, a narrow beam angle and good color mixing. As shown in Figure 13, some designs use surface texture or mini-pillows on the lens surface for color mixing to improve the color uniformity of the light beam. Figure 13: Example mini-pillow TIR optic Cree Proprietary CONFIDENTIAL Figure 14 shows the secondary optics for the XP-E MR16. Figure 14: Secondary TIR optics for XP-E MR16 4. CALCULATE THE NUMBDER OF LEDS The XLamp XP-E LED offers various efficacies depending on color temperature, bin and drive conditions. Based on the electrical data and optical output from Cree s Product Characterization Tool (PCT), 8 we chose to work with the Q2 flux bin at 3000K CCT, highlighted in yellow in Figure 15 below, to give a close color point to a halogen bulb. The PCT data indicate that an MR16 lamp containing 3 XP-E LEDs is capable of meeting the design goals. 8 The analysis came from Cree s Product Characterization Tool. property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 9

11 Prototyping Details 1. We verified the component dimensions to ensure a correct fit. Figure 16: XP-E MR16 components 2. Following the XLamp XP-family recommendations 9, we reflow soldered the XP-E LEDs onto the MCPCB with an appropriate solder paste and reflow profile and cleaned the flux residue with isopropyl alcohol. 3. We applied a thin layer of thermal conductive compound to the back of the MCPCB and secured the MCPCB to the heat sink with screws. 4. We inserted the driver into the GU5.3 plug end and soldered the DC output wires to the corresponding terminals on the MCPCB. 5. We connected the GU5.3 plug end to the heat sink and secured it with screws. We verified that the MCPCB and plug end were secure. 6. We inserted the TIR optics, ensuring proper alignment to the LEDs. Depending on the type of TIR optics and their design, various securing options can be used including self locking, additional locking ring, or adhesive. 7. We tested the completed assembly with 12 VDC. Results Optical Results Optical testing of the XLamp XP-E MR16 shows this reference design meets the target specifications. Contour plots of color and luminance distribution of the reference design 10 are shown below in Figure 17 and Figure 18. These demonstrate that the TIR optics evenly distribute the light from the 3 XP-E LEDs and produce smooth light without hotspots. 9 Cree XLamp XP Family Soldering & Handling 10 Plots were taken with Radiant Imaging s imaging photometer. property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 11

12 Figure 17: Contour plot of CCT color distribution (oval shape is a result of off-axis camera placement) Figure 18: Contour plot of luminance distribution (oval shape is a result of off-axis camera placement) property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 12

15 CONCLUSIONS The intent of this design is to demonstrate that Cree s high-power XLamp XP-E LED can be easily incorporated into a MR16 retrofit lamp meeting the ENERGY STAR requirements. Testing of the prototype shows that this goal has been met. Despite the plug and play nature of this design, there are many improvements a committed design team with appropriate resources can make, such as a simpler and cheaper heat sink and a dimmable power supply. This design shows the level of performance that can be achieved with the Cree XLamp XP-E LED but should not be interpreted as the only way that a good XP-E LED-based MR16 lamp can be designed. property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. 15

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